Although I did eventually write this fifth edition, I never would have done it without the encouragement and support of many friends and colleagues. It was Lu Han of Taylor & Francis who eventually managed to push me over the edge—in the nicest possible way. And then there are four people, whose identities are hidden from me, but, since they are all clearly expert in thinfilm optics, must certainly be people I know well. Their constructive comments based on my proposal and initial efforts were enormously helpful. I owe them and Lu a special debt of grateful thanks.